Many older garage doors have extension springs. Mine do. These are springs on either side of the door that extend when the door is closed and assist in opening and closing the door by counter-balancing much of the weight (a garage door can weigh several hundred pounds). If you have such a door take a look at the springs when the door is closed. Imagine what would happen if such a spring broke.
What could happen is bits of metal could go flying at high speed, in any direction, causing great damage to anyone or anything in their paths. Your car or your eye could be at risk, among other things. Three springs on my doors have broken in the last few years, two of them recently. Fortunately nothing got damaged and nobody got hurt. That’s because I installed a simple safety system. I’m glad I did. You should too, if you don’t have one. It is easy, inexpensive, and won’t take much time.
The system is explained on a few websites (Check This House, Ezine Articles). Here’s a brief summary: run a cable down the middle of the spring and secure the cable at both ends to a stationary structure of the garage: a wall, the ceiling, part of the metalwork of the garage door system, anything that is solid, won’t move, and is clear of the moving parts of the door and any objects or things you care about (your car, your eye).
With such a safety cable installed, when the spring breaks (and someday it will) the pieces will fly apart but can only fly along the cable. When I found my broken springs all spring pieces were sitting on the safety cable. Nothing got damaged. Nobody was at risk.